Agglomerate abrasive grains and methods of making the same

ABSTRACT

An abrasive agglomerate includes a plurality of abrasive grains bonded together in a three-dimensional structure by a substantially continuous, non-porous inorganic binder, wherein the abrasive grains have an average size of between about 0.5 microns and about 1500 microns, the inorganic binder is less than about 75 percent, by weight, of the abrasive agglomerate, and the bulk density of the abrasive agglomerate is less than about 90 percent of the bulk density of the abrasive grains.

FIELD OF INVENTION

This invention relates to abrasive agglomerates that can be used in avariety of abrasive articles, including bonded abrasives, coatedabrasives, nonwoven abrasives, and abrasive brushes.

BACKGROUND

Abrasive grits or grains have long been used in abrasive articles,including coated abrasives, bonded abrasives, and non-woven abrasives.Abrasive grits traditionally have comprised fine particles of a hardsubstance, such as alumina, alumina zirconia, diamond, cubic boronnitride, and sol-gel-derived abrasive particles. Criteria used inevaluating the effectiveness of a particular abrasive particle used fora particular abrading application typically include abrading life, rateof cut, substrate surface finish, grinding efficiency, and product cost.

Such traditional grits are effective in the removal of material from aworkpiece for a short period of time, however many grits become smoothedor polished over time such that little additional material is removed.When a substantial number of the abrasive grits become smoothed, theabrasive article typically becomes less effective in abrading theworkpiece. Moreover, as more and more of the abrasive grits becomesmoothed over time, the cut rate of the abrading article may becomeinconsistent.

To address the inconsistent cut rates over time, abrasive agglomerateshave been developed. Abrasive agglomerates have a plurality of abrasivegrits held together with an organic or inorganic binder. The binder isusually more friable than the abrasive grits so that the binderfractures to release used-up abrasive grits before they become smoothedor polished, exposing fresh abrasive grits to the workpiece.

SUMMARY

In one aspect, the present disclosure provides an abrasive agglomeratecomprising a plurality of abrasive grains bonded together in athree-dimensional structure by a substantially continuous, non-porousinorganic binder, wherein the abrasive grains have an average size ofbetween about 0.5 microns and about 1500 microns, the inorganic bindercomprises less than about 75 percent, by weight, of the abrasiveagglomerate, and the bulk density of the agglomerate is less than about90 percent of the bulk density of the abrasive grains.

In another aspect, the present disclosure provides a coated abrasivecomprising a backing having a surface, and a plurality of abrasiveagglomerates secured to the surface by a bond system, wherein each ofthe plurality of abrasive agglomerates include a plurality of abrasivegrains bonded together in a three-dimensional structure by asubstantially continuous, non-porous inorganic binder, wherein theabrasive grains have an average size of between about 0.5 microns andabout 1500 microns, the inorganic binder is less than about 75 percent,by weight, of the abrasive agglomerate, and the bulk density of theagglomerate is less than about 90 percent of the bulk density of theabrasive grains.

In another aspect, the present disclosure provides a method of makingabrasive agglomerates including the steps of providing a plurality ofglass bodies, each glass body having a defined shape, the glass bodieshaving a softening temperature, providing a plurality of abrasivegrains, mixing the plurality of glass bodies with the plurality ofgrains to form a mixture, heating the mixture to the softeningtemperature so that the glass bodies soften while substantiallyretaining the defined shape, adhering abrasive grains to the softenedglass bodies to form a plurality of abrasive agglomerates, and coolingthe abrasive agglomerates so that the glass bodies harden.

The abrasive agglomerates of the present disclosure are generallyinexpensive to manufacture and typically provide improved grinding life.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a representative abrasive agglomerateaccording to the present disclosure.

FIG. 2 is a photomicrograph of an abrasive agglomerate according to thepresent disclosure, wherein the glass binder is made from a fibrousglass body.

FIG. 3 is a photomicrograph of an abrasive agglomerate according to thepresent disclosure, wherein the glass binder is made from a glass bodyof post-consumer recycled glass.

FIG. 4 is a photomicrograph of an abrasive agglomerate according to thepresent disclosure, wherein the glass binder is made from fiberglass.

FIG. 5 is a cross-sectional schematic view of a coated abrasive articlemade with the abrasive agglomerates of the present disclosure.

FIG. 6 is a perspective view of a bonded abrasive article made with theabrasive agglomerates of the present disclosure.

FIG. 7 is an enlarged schematic view of non-woven abrasive article madewith the abrasive agglomerates of the present disclosure.

FIGS. 8 and 9 are line graphs showing the grinding results of a coatedabrasive disc made with various abrasive agglomerates made according tothe present disclosure compared with a coated abrasive disc made withconventional abrasive grains.

DETAILED DESCRIPTION

Turning to FIG. 1, an abrasive agglomerate according to the presentdisclosure comprises a plurality of abrasive grains bonded together in athree-dimensional structure by a substantially continuous, non-porousinorganic binder 14, wherein abrasive grains have an average sizebetween about 0.5 microns and about 1500 microns, inorganic binder 14 isless than about 75 percent, by weight, of abrasive agglomerate, and thebulk density of abrasive agglomerate is less than about 90 percent ofthe bulk density of abrasive grains. Here, “bulk density” refers to thevolume of a bulk amount of particles, i.e., abrasive grains or abrasiveagglomerates, when the particles are loosely packed.

In some embodiments, the inorganic binder is a glass binder formed frominexpensive raw material such as glass bodies made from choppedfiberglass strands, fiberglass insulation, post-consumer recycled glass,or sized glass frit particles. As described below, the method of thepresent invention provides for the manufacture of inexpensive abrasiveagglomerate abrasive grains using inexpensive raw materials to act as abinder for the formation of the abrasive agglomerates.

By substantially continuous and nonporous it is meant that the glassbinder is formed of a single non-porous body of glass. In thethree-dimensional structure of the abrasive agglomerate the glass binderis substantially uninterrupted throughout the three-dimensionalstructure. The glass binder generally wets the abrasive grains withoutthe formation of gaps or air pores. In some embodiments, the glassbinder is formed from a single non-porous body of glass. In someembodiments, the abrasive agglomerate has the same general shape as thebody of glass used to form the glass binder.

In some embodiments, the abrasive agglomerate has a size between about 5microns and about 10,000 microns. In some embodiments, the abrasiveagglomerate has a size between about 10 microns and about 100 microns.In yet further embodiments, the abrasive agglomerate has a size of about15 microns. By “size” of the abrasive agglomerate it is meant thesmallest linear dimension of the abrasive agglomerate. For example, thesize of the abrasive agglomerate shown in FIG. 1 is the dimension W. Inanother embodiment, abrasive agglomerates have an aspect ratio ofgreater than 1:1. In some embodiments, abrasive agglomerates have anaspect ratio of between about 1:1 and about 20:1. In yet furtherembodiments, abrasive agglomerates have an aspect ratio between about2:1 and about 5:1. By “aspect ratio” it is meant the ratio between thelongest dimension and the narrowest dimension of the abrasiveagglomerate. For example, in FIG. 1, the longest dimension of theabrasive agglomerate is length L and the shortest dimension is width W,so that the aspect ratio of the abrasive agglomerate in FIG. 1 is L:W(shown as about 3:1 in FIG. 1).

For each abrasive agglomerate, there should be a sufficient number ofabrasive grains so that an abrasive article made from abrasiveagglomerates will have an acceptable cutting life without having moreabrasive grains than are necessary for efficient grinding. In someembodiments, there are between about 3 and about 300 abrasive grains perabrasive agglomerate. In some embodiments, there are about 3 and about20 abrasive grains per abrasive agglomerate. In yet further embodiments,there are between about 3 and about 15 abrasive grains per abrasiveagglomerate. In some embodiments, there is between about 0.05 grams andabout 0.5 grams of the glass binder per gram of the abrasive grains. Insome embodiments, there are between about 0.1 grams and about 0.45 gramsof the glass binder per gram of the abrasive grains. In yet furtherembodiments, there are between about 0.15 grams and about 0.25 grams ofthe glass binder per gram of abrasive grains in the abrasiveagglomerates.

Abrasive agglomerates of the present disclosure have been shown tosubstantially increase the grinding life of an abrasive article thatemploys abrasive agglomerates rather than conventional abrasive grains.See, for example, the comparison between the grinding discs ofComparative Example B (traditional abrasive grains) and Example 15(abrasive agglomerate of the present invention). The grinding disc madewith abrasive agglomerates of the present invention were able to grind atotal of 289 grams off a 1018 steel workpiece over an 8 minute period,while a traditional grinding disc was only able to grind a total ofabout 260 grams over the same period. Also, in another comparison test,the conventional grinding disc was only able to grind for about 11minutes, while a grinding disc made with abrasive agglomerates was stillgrinding effectively after 15 minutes (see FIG. 8).

In some embodiments, abrasive grains are not substantially encapsulatedby an inorganic binder. In this context, the phrase “not substantiallyencapsulated” means that a portion of the surface of the abrasive grainis not in contact with the glass binder. In some embodiments, a majorityof each abrasive grain is exposed so that it is not encapsulated withinthe glass binder. In another embodiment, abrasive grains form adiscontinuous coating on the glass binder, wherein a straight line, suchas straight line 16 shown in FIG. 1, extending radially outwardly fromthe center of the glass binder passes through no more than threeabrasive grains. In some embodiments, abrasive grains form adiscontinuous coating on the glass binder, wherein a straight line, suchas a straight line shown in FIG. 1, extending radially outwardly fromthe center of the glass binder passes through no more than two abrasivegrains. In some embodiments, abrasive grains form a discontinuousmonolayer on the glass binder so that the line extending radiallyoutwardly from the agglomerate center passes through no more than oneabrasive grain. Because the abrasive grains form a discontinuouscoating, it is possible that the line extending outwardly from theagglomerate center may not extend through any abrasive grains, such asline 16 b shown in FIG. 1.

Abrasive grains useful in the abrasive agglomerate of the presentdisclosure are selected to achieve a desired cut rate and surface finishto be produced by the abrasive article. Abrasive grains typically have aparticle size ranging from about 0.5 micrometers to about 1500micrometers. In some embodiments, the abrasive grain particle size isbetween about 1 micrometer and about 1300 micrometers, where “size” ofabrasive grain refers to the shortest dimension of an individualparticulate abrasive grain.

Examples of suitable abrasive grains for use in abrasive agglomerates ofthe present disclosure include particles made from fused aluminum oxide,ceramic aluminum oxide, heat treated aluminum oxide, white fusedaluminum oxide, brown fused aluminum oxide, monocrystalline fusedaluminum oxide, silica, silicon carbide, green silicon carbide, boroncarbide, titanium carbide, alumina zirconia, fused alumina zirconia,diamond, ceria, cubic boron nitride (CBN), boron oxides in the form ofB₆O and B₁₀O, garnet, tripoli, boron carbonitride, sintered alphaalumina-based abrasive particles, boehmite-derived, sintered alumina,and combinations thereof. In one embodiment, abrasive grains are grainssold under the trade designation “CUBITRON” by 3M Company (St. Paul,Minn.).

In some embodiments, abrasive grains are or substantially comprise“superabrasive” materials having a hardness of at least about 35 GPa. Insome embodiments, abrasive grains are or substantially comprise“superabrasive” materials having a hardness at least about 40 GPa, suchas diamond, CBN, or combinations thereof. In this context, substantiallycomprise superabrasive materials is used to described embodiments wherethe abrasive grains are at least 30 percent superabrasive grains. Insome embodiments, the abrasive grains are at least 50 percentsuperabrasive grains. In yet further embodiments, the abrasive grainsare at least about 75 percent superabrasive grains.

In one embodiment, the glass binder is a substantially continuous,non-porous vitreous substance, which binds abrasive grains together toform the abrasive agglomerate. The glass binder should be strong enoughto hold the abrasive grains in place when the abrasive agglomerates arebeing used to abrade a workpiece, yet friable enough to break when anabrasive grain becomes too polished or dull to effectively cut theworkpiece. The glass binder is typically less than about 75 percent byweight of the abrasive agglomerate. In some embodiments, the glassbinder is less than about 60 percent by weight of the abrasiveagglomerate. In yet further embodiments, the glass binder is less than50 percent by weight of the abrasive agglomerate. Use of the term “theglass binder” is not intended to limit the glass binder solely tostrictly glassy, non-crystallized substances. Rather, the glass bindermay be a partially or fully crystallized material in the finishedabrasive agglomerate. In one embodiment, the glass binder is made fromglass bodies which start as glass, but which are partially or completelycrystallized during the heating and cooling process of making theabrasive agglomerates.

Examples of materials that may be used for the glass binder includesilicates, soda lime silicates, calcium silicates, calcium aluminosilicates, sodium silicate, potassium silicates, borosilicates,phosphates, boron glasses, aluminates, glass ceramics, titanatecontaining glasses, rare earth oxide glasses, zirconia based glasses,cullet and crushed post consumer recycled glass or combinations thereof.The glass binder may be partially or fully crystallized in the abrasiveagglomerate.

In some embodiments, the glass binder is formed from glass bodies, whichcan be obtained as inexpensive raw materials for use in forming theabrasive agglomerates. Examples of glass body raw materials includechopped fiberglass strand available from Owens Coming (Toledo, Ohio) orfrom Saint-Gobain Vetrotex America, Inc. (Valley Forge, Pa.), fiberglassinsulation batting available from Johns Manville Corporation (Denver,Colo.), recycled glass fines available from American Specialty GlassInc. (North Salt Lake City, Utah.), or glass frit pieces available fromFerro Corporation (Cleveland, Ohio). In one embodiment, glass bodies areglass fibers that may be bundled together before mixing with abrasivegrains. In some embodiments, the glass bodies are at least about 2 timeslarger than the abrasive grains. In some embodiments, the glass bodiesare at least about 3 times larger. In yet further embodiments, the glassbodies are at least about 5 times larger than abrasive grains. In thiscontext, the term “larger” is meant that the longest dimension of glassbody, i.e. length L in FIG. 1, is greater than the size of abrasivegrains.

A method of making a plurality of abrasive agglomerates includes thesteps of providing a plurality of glass bodies made from the glassbinder, each glass body having a defined shape, and glass bodies havinga softening temperature, providing a plurality of abrasive grains,mixing the plurality of glass bodies and the plurality of abrasivegrains together to form a mixture, heating the mixture to the softeningtemperature of glass bodies so that glass bodies soften whilesubstantially retaining the defined shape, adhering abrasive grains tothe softened glass bodies to form a plurality of abrasive agglomerates,and cooling abrasive agglomerates so that the glass binder of glassbodies hardens.

In some embodiments, glass bodies are provided as inexpensiveprecursors: such as chopped fiberglass strand; a plurality of glassfibers, or particles of post-consumer recycled glass. Such glass bodieshave an initial shape, which is conducive to the formation of abrasiveagglomerates. In some embodiments, the glass bodies are long, thinchopped fiberglass strands, such as the fiberglass strand sold by OwensComing, having a length of between about 1/32 inch and about ⅜ inch. Insome embodiments, the glass bodies have a length of about 1/16 inch. Insome embodiments, the width of the glass bodies is between about 1/64inch and about 1/16 inch. In some embodiments, the width of the glassbodies is about 1/32 inch. In other embodiments, the glass bodies arepost-consumer recycled glass fines having a size of between about 1/128inch and about 1/16 inch. In some embodiments, the recycled glass finescan be between about 1/64 inch and about 1/32 inch. In yet furtherembodiments, recycled glass fines having a size of about 1/64 inch canbe used.

After glass bodies have been selected, the glass bodies are mixed with aplurality of abrasive grains. In some embodiments, excess abrasivegrains are mixed with the glass bodies during the mixing step. By“excess” it is meant that more abrasive grains are mixed with the glassbodies than are needed for the formation of abrasive agglomerates. Inone embodiment, the mixing step includes providing an excess of abrasivegrains of at least about 2 parts abrasive grains per part glass bodies,by volume. In yet further embodiments, the mixing step includesproviding an excess of abrasive grains of at least about 3 partsabrasive grains per part glass bodies, by volume. In yet still furtherembodiments, the mixing step includes providing an excess of abrasivegrains of at least about 4 parts abrasive grains per part glass bodies,by volume. In another method, between about 2 parts and about 200 partsof abrasive grains, by weight, are provided per part glass bodies. Infurther embodiments, between about 10 parts and about 100 parts abrasivegrain per part glass bodies, by weight, are provided per part glassbodies. In yet still further embodiments, between about 10 parts andabout 25 parts abrasive grain per part glass bodies, by weight, areprovided per part glass bodies. The mixture of glass bodies and abrasivegrains is mixed together, i.e. using conventional mixing means such as acommercial mixer, until there is a substantially uniform distribution ofglass bodies within abrasive grains.

In some embodiments, the mixing step includes mixing water, or someother temporary liquid binder, with glass bodies and abrasive grains sothat abrasive grains and glass bodies remain uniformly mixed. In someembodiments, between about 1 gram and about 5 grams are added per 100grams of abrasive grains. In some embodiments, between about 2 grams andabout 4 grams are added per 100 grams of abrasive grains. In yet furtherembodiments, about 3 grams of water were added per 100 grams of abrasivegrains.

After being mixed, the mixture is heated to the softening temperature ofthe glass binder of glass bodies. The mixture may be heated using anyone of a number of heating devices, including furnaces and kilns. In apreferred method, the mixture is continually fed to a rotary kiln or avertical shaft kiln while formed abrasive agglomerates are removed fromthe kiln.

The mixture is heated to at least the softening temperature of the glassbinder so that glass bodies soften allowing abrasive grains to adhere toglass bodies. By “softening temperature” it is meant the temperature atwhich the viscosity of the glass binder becomes low enough for the glassbinder to be sufficiently deformable so that abrasive grains may beembedded in the glass binder. Although glass bodies may show somedistortion, fusion or flow after agglomeration when compared to theirinitial raw material state, the shape of each glass body substantiallyretains its bulk shape and remains approximately intact forming thebackbone of abrasive agglomerate.

The softening temperature of a particular the glass binder depends onthe composition of the glass binder. For example, a chopped strandfiberglass available from St. Gobain (Valley Forge, Pa.) is made from “EGlass” having a composition of 52-62 percent silica (SiO₂), 16-30percent terrous oxides (i.e. CaO or MgO), 0-10 percent B₂O₃, 11-16percent Al₂O₃ and small amounts (i.e. nor more than 3 percent) ofalkaline oxides (i.e. Na₂O or K₂O), TiO₂, Fe₂O₃, and F₂ has a softeningtemperature of about 1 000° C., while post-consumer recycled glass has adifferent composition and has a lower softening temperature of about800° C. The softening temperature of a particular glass binder canreadily be determined by one having ordinary skill in the art by trialand error, wherein the mixture of glass bodies and abrasive grains areheated to an experimental temperature, and the resulting abrasiveagglomerates are analyzed to determine if the glass binder has softenedsufficiently so that it flows adequately to wet abrasive grains suchthat the abrasive grains will be sufficiently bound to glass bodies. Inone method, the softening temperature is determined to be thetemperature wherein the glass bodies become soft enough so that at leastabout 5 percent of the abrasive grain is embedded in the glass binderfor a majority of the abrasive grains. In some embodiments, thesoftening temperature is determined to be the temperature wherein glassbodies become soft enough so that at least about 10 percent of theabrasive grain is embedded in the glass binder for a majority of theabrasive grains. In yet further embodiments, the softening temperatureis determined to be the temperature wherein glass bodies become softenough so that at least about 20 percent of the abrasive grain isembedded in the glass binder for a majority of the abrasive grains. Inone method, the mixture is heated to a temperature of between about 300°C. and about 1500° C. In some embodiments, the mixture is heated to atemperature between about 400° C. and about 1100° C. In furtherembodiments, the mixture is heated to a temperature between about 600°C. and 1000° C.

The heating step may also include heating the mixture of glass bodiesand abrasive grains above the softening temperature of the glass binderso that the glass binder flows slightly and wets the surfaces ofabrasive grains. In some embodiments, the mixture is heated to betweenabout 1° C. and about 200° C. above the softening temperature of theglass binder. In some embodiments, the mixture is heated to betweenabout 5° C. and about 50° C. above the softening temperature of theglass binder. In yet further embodiments, the mixture is heated to about10° C. above the softening temperature of the glass binder. The mixtureis heated to a temperature that is well below the melting temperature ofabrasive grains so that abrasive grains retain their size and shape, andalso so that abrasive grains do not melt or adhere to each other.

Glass bodies and abrasive grains are heated for a period of time that issufficient to ensure that a defined desired number of abrasive grainsare bound to each glass body. The amount of time in which the mixture isheated should not be too long however, as that would require more energythan is necessary for the formation of abrasive agglomerates. In someembodiments, the glass bodies and abrasive grains are heated for betweenabout ½ hour and about 4 hours. In some embodiments, the glass bodiesand abrasive grains are heated for between about 1 hour and about 3hours. In yet further embodiments, glass bodies and abrasive grains areheated for about 2 hours. However, the amount of time in which themixture of glass bodies and abrasive grains are heated depends on thetemperature to which the mixture is to be heated and the composition ofthe glass binder. If a rotary kiln is used to heat the mixture, asdescribe below, the kiln is designed so that the residence time withinthe heated portion of the rotary kiln produces the desired heating timeof the mixture. In a rotary kiln, the heating time may also be muchshorter. In some embodiments, the heating time within a rotary kiln isless than one hour. In some embodiments, the heating time within arotary kiln is between about 5 and about 15 minutes.

In some embodiments, a rotary kiln is used to heat the mixture of theglass binder and abrasive grains. In one embodiment, the rotary kilnincludes a long metal, cylindrical tube and a heating element to heatthe tube and its contents. The rotary kiln tube can be, for example, anInconel tube having an outer diameter of about 5 inches, and innerdiameter of about 4½inches, and a heated length of about 48 inches. Therotary kiln may be a 2 zoned kiln heated with silicone carbideresistance heating elements. In some embodiments, the rotary kiln isangled slightly from horizontal so that abrasive grains, the glassbinder made from glass bodies, and formed abrasive agglomerates pourdown the rotary kiln during operation. In one embodiment, the tube ofthe rotary kiln is angled from horizontal between about 2 degrees andabout 30 degrees. In some embodiments, the tube of the rotary kiln isangled from horizontal between about 5 and about 20 degrees fromhorizontal. The rotary kiln is rotated to keep the components mixedwithin the kiln during heating. In one method, the rotary kiln isrotated between about 1 and about 10 rotations per minute. In someembodiments, the rotary kiln is rotated between about 2 and about 8rotations per minute. The rotary kiln may also include a weight, whichstrikes the tube at regular intervals to prevent material from buildingup on the interior walls of the rotary kiln. The rotary kiln may alsoinclude a scraper blade within the interior of the rotary kiln for thesame purpose.

After the glass binder has been sufficiently softened, abrasive grainsadhere to glass bodies to form heated, abrasive agglomerates. Abrasivegrains that are bound to glass bodies are, in some embodiments,partially embedded in the glass binder so that a significant portion ofeach abrasive grain 12 is exposed, as shown in FIG. 1.

After heating and adhering abrasive grains to the glass binder, abrasiveagglomerates are cooled so that the glass binder hardens and abrasivegrains are held in place to form abrasive agglomerates. Abrasiveagglomerates are cooled to a temperature that is sufficiently low forthe glass binder to harden into a solid or substantially solid state toinhibit removal of abrasive grains from abrasive agglomerate. Afterglass bodies have cooled and hardened, abrasive grains are bonded ontothe outside surfaces of glass bodies. In one embodiment, abrasiveagglomerates are cooled to between about 20° C. and about 100° C. Insome embodiments, abrasive agglomerates are cooled to between about 25°C. and about 75° C. In yet further embodiments, abrasive agglomeratesare cooled to “room temperature,” or about 25° C. Cooling may beachieved by removing the formed abrasive agglomerate precursors from thefurnace or kiln and allowing them to “air cool,” or the abrasiveagglomerate precursors may be cooled by active cooling, such as with awater cooling system which cools a portion of the rotary kiln. After thecooling step, glass bodies are, in some embodiments, substantiallycontinuous and non-porous.

In another embodiment, a step of heat-treating abrasive agglomerates tocrystallize all or part of the glass binder may be included. Theheat-treating step may be employed either before or after abrasiveagglomerates have been fully cooled.

As described above, in some embodiments glass bodies used to makeabrasive agglomerates are mixed with an excess of abrasive grains sothat each glass body is sufficiently covered with abrasive grains.Therefore, in one method, a step of separating abrasive agglomeratesfrom the excess abrasive grains is included. One separating stepincludes selecting a mesh screen with openings smaller than abrasiveagglomerates, yet larger than abrasive grains, and sifting abrasiveagglomerates from the excess abrasive grains using the mesh screen.Because abrasive agglomerates may form with different sizes, in someembodiments a series of mesh screens is employed, each beingsuccessively smaller, to first catch large abrasive agglomerates, thensmaller abrasive agglomerates, while still sifting out the excessabrasive grains.

Abrasive agglomerates may have a particle size that is desired foremployment in a particular abrasive article. However, in some methods,some of glass bodies may be larger than the desired agglomerate size, ortwo or more glass bodies may stick together during the heating step sothat some of the abrasive agglomerates may be larger than desired.Therefore, in one method, a step of breaking the formed abrasiveagglomerates into smaller sizes is included. The breaking step mayinclude crushing the abrasive agglomerates under rollers or some otherbreaking means followed by sifting of abrasive agglomerates usingscreens to remove abrasive agglomerates, which are of the desired sizeso that abrasive agglomerates, which are still too large may be brokenup again. In one embodiment, the final abrasive agglomerates have a sizebetween about 5 microns and about 10,000 microns.

Abrasive agglomerates of the present invention may be used in themanufacture of several kinds of abrasive articles, such as a coatedabrasive article 30, shown in FIG. 5, bonded abrasives, such as thegrinding wheel 50 shown in FIG. 6, and a non-woven abrasive article 60,as shown in FIG. 7, and abrasive brushes.

Turning to FIG. 5, a coated abrasive article 30 is shown having abacking 32 with a major surface 34, and a plurality of abrasiveagglomerates 10 secured to major surface 34 by a bond system 36, whereineach abrasive agglomerate 10 includes a plurality of abrasive grainsbonded together in a three-dimensional structure by a substantiallycontinuous, non-porous inorganic binder, wherein the abrasive grainshave an average size of between about 0.5 microns and about 1500microns, the inorganic binder is less than about 75 percent, by weight,of abrasive agglomerate 10, and the bulk density of abrasive agglomerate10 is less than about 90 percent of the bulk density of the abrasivegrains.

Bond system 36 binds abrasive agglomerates 10 to major surface 34 ofbacking 32 to form an abrasive layer 38. As is generally known in theart, bond system 36 may comprise a make layer 40 and a size layer 42,wherein make layer 40 is applied to major surface 34 and a portion ofeach abrasive agglomerate 10 is imbedded in make layer 40. Size layer 42is applied over make layer 40 and abrasive agglomerates 10 to reinforcethe adhesion of abrasive agglomerates 10 to backing 32. A supersizelayer (not shown) may also be used.

Backing may be one of many types of backing known in the art of coatedabrasives wherein abrasive layer is coated on a major surface ofbacking. Examples of typical backing material include polymeric film,primed polymeric film, greige cloth, cloth, fiber, paper, vulcanizedfiber, nonwovens, polymer/fiber composites and treated versions and/orcombinations thereof. A preferred backing is made from cloth, such as acloth backing described in U.S. Pat. No. 5,975,988 (Christianson), thedisclosure of which is incorporated herein by reference; or a fiberbacking, such as a fiber backing described in U.S. Patent Publication2005/0032468 (Hunt et al.), the disclosure of which is incorporatedherein by reference.

Bond system is in some embodiments an organic-based bond system whichmay comprise, for example, at least two adhesive layers, the first ofwhich being make layer and the second being size layer. Typically, makelayer and size layer are formed from organic-based binder precursors,for example, resins. Precursors used to form make layer may be the sameor different from those used to form size layer. Upon exposure to theproper conditions, such as heat or an ultraviolet energy source, theresin polymerizes to form a cross-linked thermoset polymer or binder.Examples of typical resins used to form bond system include phenolicresins, aminoplast resins having pendant alpha, beta, unsaturatedcarbonyl groups, urethane resins, epoxy resins, ethylenciallyunsaturated resins, acrylated isocyanurate resins, urea-formaldehyderesins, isocyanurate resins, acrylated urethane resins, acrylated epoxyresins, bismaleimide resins, fluorine modified epoxy resins, andmixtures thereof. Epoxy and phenolic resins are preferred. Examples ofcommercially available phenolic resins include those known by the tradenames DUREZ and VACRUM available from Occidental Chemicals Corp.,RESINOX available from Monsanto, and AROFENE and AROTAP available fromAshland Chemical Co.

Aminoplast resins typically have at least one pendant alpha,beta-unsaturated carbonyl group per molecule or oligomer. Usefulaminoplast resins include those described in U.S. Pat. No. 4,903,440(Larson et al.) and U.S. Pat. No. 5,236,472 (Kirk et al.), which areincorporated herein by reference.

Epoxy resins have an oxirane ring and are polymerized by the ringopening. Suitable epoxy resins include monomeric epoxy resins andpolymeric epoxy resins and can have varying backbones and substituentgroups. In general, the backbone may be of any type normally associatedwith epoxy resins, for example, Bis-phenol A, and the substituent groupscan include any group free of an active hydrogen atom that is reactivewith an oxirane ring at room temperature. Representative examples ofsuitable substituent groups include halogens, ester groups, ethergroups, sulfonate groups, siloxane groups, nitro groups and phosphategroups.

Examples of preferred epoxy resins include2,2-bis[4-(2,3-epoxypropoxy)-phenyl]propane (a diglycidyl ether ofbisphenol) and commercially available materials under the tradedesignation “Epon 828”, “Epon 04”, and “Epon 01F” available from ShellChemical Co., and “DER-331”, “DER-332” and “DER-334” available from DowChemical Co. Other suitable epoxy resins include glycidyl ethers ofphenol formaldehyde novolac, for example, “DEN431 ” and “DEN428”available from Dow Chemical Co.

Ethylenically unsaturated resins include both monomeric and polymericcompounds that contain atoms of carbon, hydrogen, and oxygen, andoptionally, nitrogen and halogen atoms. Oxygen or nitrogen atoms or bothare generally present in ether, ester, urethane, amide, and urea groups.Ethylenically unsaturated compounds, in some embodiments, have amolecular weight of less than about 4,000, and are, in some embodiments,esters made from the reaction of compounds containing aliphaticmonohydroxy groups or aliphatic polyhydroxy groups and unsaturatedcarboxylic acids, such as acrylic acid, methacrylic acid, itaconic acid,crotonic acid, isocrotonic acid, and maleic acid.

Representative examples of acrylate resins include methyl methacrylate,ethyl methacrylate styrene, divinylbenzene, vinyl toluene, ethyleneglycol diacrylate, ethylene glycol methacrylate, hexanediol diacrylate,triethylene glycol diacrylate, trimethylolpropane triacrylate, glyceroltriacrylate, pentaerythritol triacrylate, pentaerythritol trimethocyate,pentaerythritol tetraacrylate and pentaerythritol tetramethocylate.

Other ethylenically unsaturated resins include monoallyl, polyallyl, andpolymethallyl esters and amides of carboxylic acids, such as diallylphthalate, diallyl adipate, and N,N-diallyladipamide. Other suitablenitrogen-containing compounds includetris(2-acryloyl-oxyethyl)isocyanurate,1,3,5-tri(2-methacryloxyethyl)-s-triazine, acrylamide, methylacrylamide,N-methylacrylamide, N,N-dimethylacrylamide, N-vinylpyrrolidone, andN-vinylpiperidone.

Acrylated urethanes are diacrylate esters of hydroxy terminated NCOextended polyesters or polyethers. Examples of commercially availableacrylated urethanes include “UVITHANE 782”, available from MortonThiokol Chemical, and “CMD 6600,” “CMD 8400,” and “CMD 8805,” availablefrom Radcure Specialties.

Acrylated epoxies are diacrylate esters of epoxy resins, such as thediacrylate esters of bisphenol A epoxy resin. Examples of commerciallyavailable acrylated epoxies include “CMD 3500,” “UCMD 3600,” and “CMD3700,” available from Radcure Specialties.

Bond system 36, for example, the make layer 40 and/or size layer 42, ofthis invention can further comprise optional additives, such as, forexample, fillers (including grinding aids), fibers, antistatic agents,lubricants, wetting agents, surfactants, pigments, dyes, couplingagents, plasticizers, and suspending agents. The amounts of thesematerials can be selected to provide the properties desired.

Examples of useful fillers for this invention include metal carbonates(such as calcium carbonate (e.g., chalk, calcite, marl, travertine,marble, and limestone), calcium magnesium carbonate, sodium carbonate,and magnesium carbonate); silica (such as quartz, fumed silica, glassbeads, glass bubbles, and glass fibers); silicates (such as talc, clays(e.g., montmorillonite) feldspar, mica, calcium silicate, calciummetasilicate, sodium aluminosilicate, sodium silicate); metal sulfates(such as calcium sulfate, barium sulfate, sodium sulfate, aluminumsodium sulfate, aluminum sulfate); gypsum; vermiculite; wood flour;aluminum trihydrate; carbon black; metal oxides (such as calcium oxide(lime), aluminum oxide (alumina), and titanium dioxide); and metalsulfites (such as calcium sulfite). The filler typically has an averageparticle size ranging from about 0.1 to 100 micrometers. In someembodiments, the filler has an average particle size ranging frombetween 1 to 50 micrometers. In yet further embodiments, the filler hasan average particle size ranging from between 1 and 25 micrometers.

Suitable grinding aids include particulate material, the addition ofwhich has a significant effect on the chemical and physical processes ofabrading which results in improved performance. In particular, agrinding aid may 1) decrease the friction between the abrasive grainsand the workpiece being abraded, 2) prevent the abrasive grain from“capping”, i.e. prevent metal particles from becoming welded to the topsof the abrasive grains, 3) decrease the interface temperature betweenthe abrasive grains the workpiece and/or 4) decrease the grindingforces. In general, the addition of a grinding aid increases the usefullife of the coated abrasive. Grinding aids encompass a wide variety ofdifferent materials and can be inorganic- or organic-based.

Examples of grinding aids include waxes, organic halide compounds,halide salts and metals and their alloys. The organic halide compoundswill typically break down during abrading and release a halogen acid ora gaseous halide compound. Examples of such materials includechlorinated waxes like tetrachloronaphthalene, pentachloronaphthalene;and polyvinyl chloride. Examples of halide salts include sodiumchloride, potassium cryolite, sodium cryolite, ammonium cryolite,potassium tetrafluoroborate, sodium tetrafluoroborate, siliconfluorides, potassium chloride, magnesium chloride. Examples of metalsinclude tin, lead, bismuth, cobalt, antimony, cadmium, iron, andtitanium. Examples of other grinding aids include sulfur, organic sulfurcompounds, graphite, and metallic sulfides. A combination of differentgrinding aids can be used, for example, as described in WO 95/24991(Gagliardi et al.). The above mentioned examples of grinding aids aremeant to be a representative showing of grinding aids and are not meantto encompass all grinding aids.

Examples of antistatic agents include graphite, carbon black, vanadiumoxide, humectants, and the like. These antistatic agents are disclosedin U.S. Pat. No. 5,061,294 (Harmer et al.); U.S. Pat. No. 5,137,542(Buchanan et al.); and U.S. Pat. No. 5,203,884 (Buchanan et al.)incorporated herein by reference.

Bond system, including make layer and size layer, generally has a Knoophardness number (KHN) of least 50 KHN (which can also be expressed inunits of Kg_(f)/mm²), typically at least about 60 KHN. In someembodiments, bond system, including make layer and size layer, generallyhas a Knoop hardness number (KHN) of least 50 KHN, typically at leastabout 70 KHN. In yet further embodiments, bond system, including makelayer and size layer, generally has a Knoop hardness number (KHN) ofleast 50 KHN, typically at least about 80 KHN. In still yet furtherembodiments, bond system, including make layer and size layer, generallyhas a Knoop hardness number (KHN) of least 50 KHN, typically at leastabout 90 KHN, measured in accordance with ASTM E384-89, in order to beable to withstand grinding forces and not disintegrate.

Generally, if bond system comprises make and size layers, at least oneof the make and size layers can comprise from about 5 to 95 parts byweight, in some embodiments 30 to 70 parts by weight, of a binderprecursor, for example, a thermoset resin, and between about 5 to 95parts by weight, in some embodiments, 30 to 70 parts by weight, of afiller. If bond system comprises an abrasive slurry, the amount ofbinder precursor can range from 5 to 95 weight percent and the amount offiller can range from 5 to 95 weight percent, based on the weight of theabrasive slurry.

For example, the preferred Knoop hardness number ranges for bond system,i.e., in some embodiments, at least 70 KHN. In yet further embodiments,the preferred Knoop hardness number ranges for bond system, i.e., atleast 80 KHN. In still yet further embodiments, the preferred Knoophardness number ranges for bond system, i.e., at least 90 KHN, can beachieved by the presence of filler particles, which are described above.The filler particles will harden the cured thermoset resin and toughenbond system, for example, the make and size layer. The amount of fillerparticles and the presence of a coupling agent aid in controlling theKnoop hardness of bond system.

To achieve the preferred Knoop hardness ranges, a coupling agent may bepresent on the filler and/or the abrasive particles. The coupling agentprovides an association bridge between bond system and the filler and/orabrasive particles. Examples of suitable coupling agents includeorganosilanes, zircoaluminates, and titanates. Coupling agents areusually present in an amount ranging between about 0.1 to 5 percent byweight, in some embodiments, 0.5 to 3.0 percent, based on the totalweight of the filler and the abrasive agglomerates.

Abrasive agglomerates may also be used in bonded abrasives. Bondedabrasive articles typically include a shaped mass of abrasive particles(which in practicing the present disclosure includes abrasive grainsbonded together by the glass binder to form abrasive agglomerates) heldtogether by a binder, which may be organic, metallic, or vitrified. Suchshaped mass can be, for example, in the form of a wheel, such as agrinding wheel, shown in FIG. 6, or cutoff wheel. The diameter ofgrinding wheels typically is about 1 centimeter to over 1 meter; thediameter of cut off wheels about 1 centimeter to over 80 centimeter, andmore typically between about 3 centimeter and about 50 centimeter. Thecut off wheel thickness is typically about 0.5 millimeter to about 5centimeter, more typically between about 0.5 millimeter and about 2centimeter. The shaped mass can also be in the form, for example, of ahoning stone, segment, mounted point, disc (e.g. double disc grinder) orother conventional bonded abrasive shape. Bonded abrasive articlestypically comprise about 3-50 percent by volume binder 52, about 30-90percent by volume abrasive material, up to 50 percent by volumeadditives (including grinding aids), and up to 70 percent by volumepores, based on the total volume of the bonded abrasive article.Typically, grinding wheels have at least 10 percent or more porosity.For some grinding operations, very high porosity of more than 50 percentis desirable. One example of a bonded abrasive is the grinding wheel 50shown in FIG. 6. Grinding wheel 50 includes abrasive agglomerates of thepresent invention, which are molded together in a wheel by a binder 52,wherein the bonded wheel is mounted on a hub 54.

Suitable organic binders used for making bonded abrasive articlesinclude thermosetting organic polymers. Examples of suitablethermosetting organic polymers include phenolic resins,urea-formaldehyde resins, melamine-formaldehyde resins, urethane resins,acrylate resins, polyester resins, aminoplast resins having pendantα,β-unsaturated carbonyl groups, epoxy resins, acrylated urethane,acrylated epoxies, and combinations thereof. Binder 52 and/or abrasivearticle may also include additives such as fibers, lubricants, wettingagents, thixotropic materials, surfactants, pigments, dyes, antistaticagents (e.g., carbon black, vanadium oxide, graphite, etc.), couplingagents (e.g., silanes, titanates, zircoaluminates, etc.), plasticizers,suspending agents, and the like. The amounts of these optional additivesare selected to provide the desired properties. The coupling agents canimprove adhesion to the abrasive particles and/or filler. The binderchemistry may allow for thermal curing, radiation curing, orcombinations thereof. Additional details on binder chemistry may befound in U.S. Pat. No. 4,588,419 (Caul et al.), U.S. Pat. No. 4,751,138(Tumey et al.), and U.S. Pat. No. 5,436,063 (Follett et al.), thedisclosures of which are incorporated herein by reference.

More specifically with regard to vitrified bonded abrasives, vitreousbinders 52, which exhibit an amorphous structure and are typically hard,are well known in the art. Bonded, vitrified abrasive articles may be inthe shape of a wheel, honing stone, mounted pointed or otherconventional bonded abrasive shape. A preferred vitrified bondedabrasive article is a grinding wheel.

Examples of metal oxides that are used to form vitreous binders 52include: silica, silicates, alumina, soda, calcia, potassia, titania,iron oxide, zinc oxide, lithium oxide, magnesia, boria, aluminumsilicate, borosilicate glass, lithium aluminum silicate, combinationsthereof, and the like. Typically, vitreous binders 52 can be formed fromcomposition comprising from 10 to 100 percent glass frit, although moretypically the composition comprises percent 20 to 80 percent glass frit,or 30 percent to 70 percent glass frit. The remaining portion of thevitreous binder 52 can be a non-frit material. Alternatively, vitreousbinder 52 may be derived from a non-frit containing composition.Vitreous binders 52 are typically matured at a temperature(s) in therange from about 700° C. to about 1500° C., usually in the range fromabout 800° C. to about 1300° C., sometimes in the range from about 900°C. to about 1 200° C., or even in the range from about 950C. to about 1100° C. The actual temperature at which the bond is matured depends, forexample, on the particular bond chemistry. Vitrified binder 52 may alsobe heat treated to cause it to partially or completely crystallize.

Vitrified binders may include those comprising silica, alumina (in someembodiments, at least 10 percent by weight alumina), and boria (in someembodiments, at least 10 percent by weight boria). In most cases thevitrified binder further comprise alkali metal oxide(s) (e.g., Na₂O andK₂O) (in some cases at least 10 percent by weight alkali metaloxide(s)).

Binder 52 may also contain filler materials or grinding aids, typicallyin the form of a particulate material. Typically, the particulatematerials are inorganic materials. Examples of useful fillers for thisinvention include: metal carbonates (e.g., calcium carbonate (e.g.,chalk, calcite, marl, travertine, marble and limestone), calciummagnesium carbonate, sodium carbonate, magnesium carbonate), silica(e.g., quartz, glass beads, glass bubbles and glass fibers) silicates(e.g., talc, clays, (montmorillonite) feldspar, mica, calcium silicate,calcium metasilicate, sodium aluminosilicate, sodium silicate) metalsulfates (e.g., calcium sulfate, barium sulfate, sodium sulfate,aluminum sodium sulfate, aluminum sulfate), gypsum, vermiculite, woodflour, aluminum trihydrate, carbon black, metal oxides (e.g., calciumoxide (lime), aluminum oxide, and titanium dioxide), and metal sulfites(e.g., calcium sulfite). Sulfur or wax based grinding aids may also beadded to a bonded wheel by filling the porosity after it is has beenformed.

In general, the addition of a grinding aid increases the useful life ofthe abrasive article. A grinding aid is a material that has asignificant effect on the chemical and physical processes of abrading,which results in improved performance. Although not wanting to be boundby theory, it is believed that a grinding aid(s) will (a) decrease thefriction between the abrasive material and the workpiece being abraded,(b) prevent the abrasive particles from “capping” (i.e., prevent metalparticles from becoming welded to the tops of the abrasive particles),or at least reduce the tendency of abrasive particles to cap, (c)decrease the interface temperature between the abrasive particles andthe workpiece, or (d) decreases the grinding forces.

Turning to FIG. 7, non-woven abrasive articles of the present disclosureinclude an open porous lofty polymer filament structure having abrasiveagglomerates distributed throughout the structure and adherently bondedtherein by an organic binder 64. Examples of filaments include polyesterfibers, polyamide fibers, and polyaramid fibers. In FIG. 7, a schematicdepiction, enlarged about 100×, of a typical non-woven abrasive article60 is provided. Such a non-woven abrasive article comprises fibrous mat62 as a substrate, onto which abrasive agglomerates are adhered by abinder 64. Binder 64 used for non-woven abrasive article 60 may be oneof the same organic binders described above for bonded abrasives.

Useful abrasive brushes include those having a plurality of bristlesunitary with a backing (see, e.g., U.S. Pat. No. 5,427,595 (Pihl etal.), U.S. Pat. No. 5,443,906 (Pihl et al.), U.S. Pat. No. 5,679,067(Johnson et al.), and U.S. Pat. No. 5,903,951 (lonta et al.)), thedisclosure of which is incorporated herein by reference). In someembodiments, such brushes are made by injection molding a mixture ofpolymer and abrasive particles (which in practicing the presentinvention includes abrasive grains agglomerated together by the glassbinder in the form of abrasive agglomerates according to the presentdisclosure).

Whether they are coated abrasives, bonded abrasives, non-wovenabrasives, or abrasive brushes, the abrasive articles can contain 100percent abrasive agglomerates according to the present disclosure, orblends of abrasive agglomerates with other abrasive particles (which mayalso be agglomerated) and/or diluent particles. However, at least about2 percent by weight, in some embodiments at least about 5 percent byweight, and in yet further embodiments, between about 30 percent andabout 100 percent by weight, of the abrasive particles in the abrasivearticles are abrasive agglomerates. In some instances, abrasiveagglomerates may be blended with other abrasive particles and/or diluentparticles at a ratio of between 5 to 75 percent by weight, about 25 to75 percent by weight, about 40 to 60 percent by weight, or about 50percent to 50 percent by weight (i.e., in equal amounts by weight).Examples of suitable abrasive particles include, but are not limited to,fused aluminum oxide (including white fused alumina, heat treatedaluminum oxide and brown aluminum oxide), silicon carbide, siliconnitride, boron carbide, titanium carbide, diamond, cubic boron nitride,garnet, fused alumina-zirconia, sol-gel-derived abrasive particles, andthe like. The sol-gel-derived abrasive particles may be seeded ornon-seeded. Likewise, the sol-gel-derived abrasive particles may berandomly shaped or have a shape associated with them, such as a triangleor rod. Examples of sol gel abrasive particles include those describedabove. Abrasive agglomerate may have the essentially the same size asthe diluent particle, or conversely, abrasive agglomerate may be largeror smaller in size than the diluent particle.

Abrasive agglomerates according to the present invention can also becombined with other abrasive agglomerates. The binder of the otherabrasive agglomerates may be organic and/or inorganic. Additionaldetails regarding abrasive agglomerates may be found, for example, inU.S. Pat. No. 4,311,489 (Kressner), U.S. Pat. No. 4,652,275 (Bloecher etal.), U.S. Pat. No. 4,799,939 (Bloecher et al.), U.S. Pat. No. 5,549,962(Holmes et al.), 5,975,988 (Christianson), U.S. Pat. No. 6,620,214(McArdle et al.), U.S. Pat. No. 6,790,126 (Wood et al.), and U.S. Pat.No. 6,881,483 (McArdle et al.), the disclosures of which areincorporated herein by reference.

If there is a blend of different types of abrasive agglomerates or ablend of abrasive agglomerates and other abrasive particles, theparticle/agglomerate types forming the blend may be of the same size.Alternatively, the particle/agglomerate types may be of differentparticle sizes.

Examples of suitable diluent particles include marble, gypsum, flint,silica, iron oxide, aluminum silicate, glass (including glass bubblesand glass beads), alumina bubbles, alumina beads and diluentagglomerates.

The abrasive agglomerates of the present disclosure may be uniformlydistributed in the abrasive article or concentrated in selected areas orportions of the abrasive article. For example, in a coated abrasive,there may be two layers of abrasive particles/grain, wherein the firstlayer comprises abrasive particles/grain other than abrasiveagglomerates according to the present invention, and the second(outermost) layer comprises abrasive agglomerates. Likewise in a bondedabrasive, there may be two distinct sections of the grinding wheel,wherein the outermost section may comprise abrasive agglomeratesaccording to the present invention, whereas the innermost section doesnot. Alternatively, abrasive agglomerates may be uniformly distributedthroughout the bonded abrasive article.

Further details regarding coated abrasive articles can be found, forexample, in U.S. Pat. No. 4,734,104 (Broberg), U.S. Pat. No. 4,737,163(Larkey), U.S. Pat. No. 5,203,884 (Buchanan et al.), U.S. Pat. No.5,152,917 (Pieper et al.), U.S. Pat. No. 5,378,251 (Culler et al.), U.S.Pat. No. 5,417,726 (Stout et al.), U.S. Pat. No. 5,436,063 (Follett etal.), U.S. Pat. No. 5,496,386 (Broberg et al.), U.S. Pat. No. 5, 609,706(Benedict et al.), U.S. Pat. No. 5,520,711 (Helmin), U.S. Pat. No.5,954,844 (Law et al.), U.S. Pat. No. 5,961,674 (Gagliardi et al.),5,975,988 (Christinason), U.S. Pat. No. 6,620,214 (McArdle et al.), U.S.Pat. No. 6,790,126 (Wood et al.), and U.S. Pat. No. 6,881,483 (McArdleet al.), the disclosures of which are incorporated herein by reference.Further details regarding bonded abrasive articles can be found, forexample, in U.S. Pat. No. 4,543,107 (Rue), U.S. Pat. No. 4,741,743(Narayanan et al.), U.S. Pat. No. 4,800,685 (Haynes et al.), U.S. Pat.No. 4,898,597 (Hay et al.), U.S. Pat. No. 4,997,461 (Markhoff-Matheny etal.), U.S. Pat. No. 5,038,453 (Narayanan et al.), U.S. Pat. No.5,110,332 (Narayanan et al.), and U.S. Pat. No. 5,863,308 (Qi et al.)the disclosures of which are incorporated herein by reference. Further,details regarding vitreous bonded abrasives can be found, for example,in U.S. Pat. No. 4,543,107 (Rue), U.S. Pat. No. 4,898,597 (Hay), U.S.Pat. No. 4,997,461 (Markhoff-Matheny et al.), U.S. Pat. No. 5,094,672(Giles et al.), U.S. Pat. No. 5,118,326 (Sheldon et al.), U.S. Pat. No.5,131,926(Rostoker et al.), U.S. Pat. No. 5,203,886 (Sheldon et al.),5,282,875 (Wood et al.), U.S. Pat. No. 5,738,696 (Wu et al.), and U.S.Pat. No. 5,863,308 (Qi), the disclosures of which are incorporatedherein by reference. Further details regarding nonwoven abrasivearticles can be found, for example, in U.S. Pat. No. 2,958,593 (Hooveret al.), the disclosure of which is incorporated herein by reference.

Methods for abrading with preferred abrasive agglomerates according tothe present invention range from snagging (i.e., high pressure highstock removal) to polishing (e.g., polishing medical implants withcoated abrasive belts), wherein the latter is typically done with finergrades (e.g., ANSI 220 and finer) of abrasive grains. Abrasiveagglomerates may also be used in precision abrading applications, suchas grinding camshafts with vitrified bonded wheels. The size of theabrasive agglomerates, and abrasive grains comprising such agglomerates,used for a particular abrading application will be apparent to thoseskilled in the art.

Abrading with abrasive agglomerates may be done dry or wet. For wetabrading, the liquid may be introduced supplied in the form of a lightmist to complete flood. Examples of commonly used liquids include:water, water-soluble oil, organic lubricant, and emulsions. The liquidmay serve to reduce the heat associated with abrading and/or act as alubricant. The liquid may contain minor amounts of additives such asbactericide, antifoaming agents, and the like.

Abrasive agglomerates may be used to abrade workpieces such as aluminummetal, carbon steels, mild steels, tool steels, stainless steel,hardened steel, titanium, nickel alloys, cobalt alloys, glass, ceramics,wood, wood like materials, paint, painted surfaces, organic coatedsurfaces and the like. The applied force during abrading typicallyranges from about 1 to about 100 kilograms.

Abrasive agglomerates may be also be used in loose form or in a slurrywherein agglomerate abrasive grain is dispersed in liquid medium (e.g.,water).

The following examples will further illustrate specific embodiments ofthe present invention. Those of ordinary skill in the art will recognizethat the present invention also includes modifications and alterationsof the embodiments set out in the examples and that the illustrativeexamples do not limit the scope of the claimed invention.

EXAMPLES Example 1

A small quantity of ¼ inch Fiberglass Chopped Strand (US Composites,Inc., West Palm Beach, Fla.) was mixed with a large excess of grade 50351 CUBITRON (3M, St. Paul, Minn.) abrasive grain in a porcelaincrucible. The crucible with this mix was placed in a muffle oven; heatedto 1100° C. and held there for 1 hour before the furnace was turned offand allowed to cool. By passing the contents through a 14 mesh screenthe agglomerates were recovered from the excess abrasive grit. Rodshaped agglomerates about 6 millimeters long (¼ inch) were recovered.SEM examination of the particles showed the glass to have flowed welland wetted the grits.

Example 2

By volume 4 parts 351 CUBITRON grain (3M, St. Paul, Minn.) was mixedwith 1 part ¼ inch fiberglass chopped strand (US Composites Inc., WestPalm Beach, Fla.). This mix was placed in 4 porcelain crucibles. Thecrucibles containing this mix were placed in a muffle oven; heated to1100° C. and held there for 75 minutes before the furnace was turned offand allowed to cool. The content of the crucibles was screened on aRotap screener with a nest of 12, 14, and 30 mesh screens. The +12 meshmaterial was lightly crushed in 4 inch roll crusher with a large (approx2-3 millimeters) roll gap. This crushed material was then screened withthe same screen nest as above. The total output was: +12 mesh 84.8g,−12+14 mesh 170.1g, −14+20 mesh 236g, −20+30 mesh, 71.5g, −30 mesh1150g. The −20+30 mesh fraction consisted of agglomerates containingabout 3 to 8 individual grits. The −30 mesh was predominately individualgrits.

Examples 3-25

TABLE 1 Glass Source Owens-Corning Owens Corning, Toledo, Ohio CS691A ⅛inch Owens-Corning Owens Corning, Toledo, Ohio CS691A 1/16 inch St.Gobain Vetrotex Saint-Gobain Vetrotex America, Inc., Chopped StrandValley Forge, Pennsylvania 97D-A4 ¼ inch Clear Plate Glass AmericanSpecialty Glass Inc., North Fines Salt Lake City, Utah Crystal ClearGlass American Specialty Glass Inc., North Fines Salt Lake City, UtahClear Bead Fines American Specialty Glass Inc., North Salt Lake City,Utah −30 mesh Silica American Specialty Glass Inc., North SandSubstitute Salt Lake City, Utah Ferro 3225 Ferro Corporation, Cleveland,Ohio Ferro 3226 Ferro Corporation, Cleveland, Ohio Ferro 3227 FerroCorporation, Cleveland, Ohio Ferro XP150 Ferro Corporation, Cleveland,Ohio Johns Manville Johns Manville Corporation, Denver, fiberglass battColorado insulation (2 inch thick)Test ProceduresSwing Arm Test

The abrasive disc to be evaluated was attached to a 20.3 centimetercircular backup plate, commercially available as Part No. 05114145192from 3M Company. The backup plate was then secured to a testing deviceobtained under the trade designation “SWING ARM TESTER” from ReelManufacturing, Centerville, Minn., using a metal screw fastener. A 1.897millimeter thick mild steel disc shaped work piece with a 30.5centimeter diameter was weighed and secured to the testing device with ametal fastener. During each test, the steel workpiece was applied to theabrasive article disc with a force of 39.2 Newtons. The abrasive articledisc was rotated at 3500 revolutions per minute (rpm), and the workpiecewas placed against the disc at an angle of 7 degrees for 8 minutes,while the workpiece was rotated at 2 rpm. The amount of steel removed(total cut) and weight loss of each abrasive disc (i.e., shelling) wasrecorded.

Slide Action Test

The Slide Action Test was designed to measure the cut rate of the coatedabrasive disc. The abrasive disc to be tested was used to grind the faceof a 1.25 centimeter by 18 centimeter 1018 mild steel workpiece. Thegrinder used was a constant load hydraulic disc grinder. The constantload between the workpiece and the abrasive disc was provided by a loadspring. The back-up pad for the grinder was an aluminum back-up pad,beveled at approximately 7 degrees, extending from the edge and intowards the center 3.5 centimeter. The disc was secured to the aluminumpad by a retaining nut and was driven at 5,500 rpm. The load between theback-up pad and disc and workpiece was about 6.8 kg. Each disc was usedto grind a separate workpiece for a 60 second interval. The initial cutwas the amount of metal removed in the first 60 seconds of grinding.Unless otherwise noted, total cut is the total amount of metal removedduring the test; total cut in grams is reported. The grindingperformance data is based on an average of three discs unless otherwisenoted.

Comparative Examples A and B

Comparative Examples A and B were “988CR Grade 50 Fibre Disc, 7 in ×⅞in”, obtained from 3M Company, St. Paul, Minn.

Examples 3-8 (fibrous glass source)

Agglomerates using fibrous glass sources were prepared as follows. 1500grams of grade 50 CUBITRON 321 (obtained from 3M, St. Paul, Minn.) and60 grams chopped glass fiber were combined and mixed together for 3minutes using a Hobart Food Mixer using a flat beater at low speed.Sufficient water was added to the mix so that the mineral/fiberglassmixture would hold together in a mass when squeezed in the palm of yourhand.

The resulting mixture was split into two equal parts and each half waspacked into an 8½ inch ×4¼ inch ×2 inch alumina sagger. The two saggerswere stacked on top of one another and placed in a Fischer Scientific“IsoTemp” programmable muffle furnace and fired to 1000° C. at heat-uprate of 5° C./min. Once the samples reached 1 000° C., they were allowedto soak at temperature for 2 hours. After 2 hours, the kiln shutdown andthe sample gradually cooled to room temperature.

Once fired, the agglomerated mixture of fiberglass and abrasiveresembled a bird's nests, which were removed from the alumina saggers.Each agglomerated mixture was placed in a topmost screen of a stack ofUSA Standard Testing Sieves consisting of a 10, 18, 20, 25, 30 meshscreens. To the #10 screen was also added numerous ½ inch aluminamilling media cylinders, which aided in the breakup of the “bird's nest”into individual agglomerates. The stack of screens was placed in a sieveshaker (“Ro-Tap Model RX-29”, W. S. Tyler Particle Analysis, Filtrationand Industrial Screening Products—Mentor, Ohio) for minutes. Theindividual screen cuts were then recovered.

The agglomerates from the −18+20 screen cut were electrostaticallycoated on fiber disc backings using a standard calcium carbon filledmake and cryolite filled size resin. A separate batch of discs wereelectrostatically coated using 50/50 w/w blend of the −20+25 and −25+30screen cut using the same the resin.

Example discs were tested using the Swing Arm Test. The results arereported in Table 2.

Examples 9 AND 10(fibrous glass source)

Examples 9 and 10 were prepared identically to Examples 3-8 except that222 Cubitron was substituted in place of 321 Cubitron.

Examples 11-14 (Recycled glass source)

Examples 11-14 were prepared using recycled glass sources. Agglomerateswere prepared by combining 1500 grams of grade 50 Cubitron 321 and 50grams recycled glass. The two components were mixed together for 3minutes using a Hobart Food Mixer using a flat beater at low speed.Sufficient water was added to the mix so that the mineral/fiberglassmixture would hold together in a mass when squeezed in the palm of yourhand.

The resulting mixture was split into two equal parts and each half waspacked into an alumina sagger. The two saggers were stacked on top ofone another and placed in a programmable Fischer Scientific Box kiln andfired to 800° C. at heat-up rate of 5° C./min. Once the samples reached800° C., they were allowed to soak at temperature for 2 hours. After 2hours, the kiln shutdown and the fired agglomerates gradually cooled toroom temperature.

The Examples were graded and subsequently coated onto fiber discs in anidentical fashion to Examples 3-8, described above.

Example discs were tested using the Swing Arm Test. The results arereported in Table 2.

Examples 15 -24 (glass frit source)

Agglomerates were prepared by combining 1500 grams of grade 50 CUBITRON321 and 50 grams of glass frit. The two components were mixed togetherfor 3 minutes using a Hobart Food Mixer using a flat beater at lowspeed. Sufficient water was added to the mix so that themineral/fiberglass mixture would hold together in a mass when squeezedin the palm of your hand.

The resulting mixture was split into two equal parts and each half waspacked into an alumina sagger. The two saggers were stacked on top ofone another and placed in a programmable Fischer Scientific Box kiln.Each lot was heated to a temperature 50° C. higher than the softeningtemperature designated above. The heat-up rate for each sample was 5°C./min. Once the examples reached temperature, they were allowed to soakat that temperature for 2 hours. After 2 hours, the kiln was shut downand the Example gradually cooled to room temperature.

The Examples were graded and coated onto fiber discs in an identicalfashion to Examples 3-8, described above except that the −18+20 fractionwas drop coated rather than electrostatically coated. Example discs weretested using the Swing Arm Test. The results are reported in Table 2.

Examples 15 -24 were tested on the Slide Action Test. Each disc wasground for 15 1-minute intervals using 1018 mild steel workpieces. Inaddition, 3M 988CR discs were included as a control for the test. Themetal removed after each minute interval was recorded and is reported inFIGS. 7 and 8.

EXAMPLE 25

Example 25 was prepared much like one would prepare lasagna. Fiberglassinsulation batting (originally 2 inches thick) was pulled apart intoseveral thin layers. Into the bottom of an individual 8½ inch ×4¼ inch ×2 inch alumina sagger, a thin layer of alumina grit was sprinkledfollowed by a layer of insulation followed by another layer of aluminagrit and then insulation. This was continued until the alternatinglayers filled the sagger. Periodically during the process, weight wasapplied to the mixture in order to tamp down the mix and therefore packmore layers into the sagger. Once two saggers were filled, they werestacked on top of one another and placed in a Fischer Scientific“IsoTemp” programmable muffle furnace and fired to 700° C. at heat-uprate of 5° C./min. Once the samples reached 700° C., they were allowedto soak at temperature for 2 hours. After 2 hours, the kiln was shutdown and the sample gradually cooled to room temperature.

After heat treatment, the mixture had shrunk to about ¼ of its originalvolume. The agglomerated “birds nest” was brittle and could easily bebroken by hand into smaller pieces which were then placed into a mortarand pestle and further ground into powder. This powder was hand siftedthrough 100 mesh USA Standard Testing screen in order to retain the −100screen fraction. This −100 screen fraction was further sifted through 66micron and 25 micron screens using a sonic sifter. A photo showing the−66 micron +25 micron screen fiberglass agglomerate is shown in FIG. 4.TABLE 2 Total Cut Weight after 8 Loss after Agglomerate Firing minutes 8minutes Example Glass Source Particle Size Temperature (grams) (grams)Comparative no Grade 50 N/A 127.0 5.9 A (988CR) agglomerates Cubitron222 3 Owens Grade 50 −18 + 20 1000 234.4 6.6 Corning Cubitron CS691A 321⅛ inch 4 Owens Grade 50 50% −20 + 25, 1000 242.4 3.6 Corning Cubitron50% −25 + 30 CS691A 321 ⅛ inch 5 Owens Grade 50 −18 + 20 1000 234.4 4.7Corning Cubitron CS691A 321 1/16 inch 6 Owens Grade 50 50% −20 + 25,1000 234.7 3.8 Corning Cubitron 50% −25 + 30 CS691A 321 1/16 inch 7 St.Gobain Grade 50 −18 + 20 1000 260.6 5.7 Chopped Cubitron Strand 32197D-A4 ¼ inch 8 St. Gobain Grade 50 50% −20 + 25, 1000 258.3 3.8 ChoppedCubitron 50% −25 + 30 Strand 321 97D-A4 ¼ inch 9 St. Gobain Grade 50−18 + 20 1000 231.9 6.4 Chopped Cubitron Strand 222 97D-A4 ¼ inch 10 St.Gobain Grade 50 50% −20 + 25, 1000 251.1 3.5 Chopped Cubitron 50% −25 +30 Strand 222 97D-A4 ¼ inch 11 Clear Plate Glass Grade 50 Cubitron 50%−20 + 25, 800 189.3 2.8 Fines 321 50% −25 + 30 12 Crystal Clear GlassGrade 50 Cubitron 50% −20 + 25, 800 200.0 2.6 Fines 321 50% −25 + 30 13Clear Bead Fines Grade 50 Cubitron 50% −20 + 25, 800 199.4 2.6 321 50%−25 + 30 14 −30 mesh Silica Sand Grade 50 Cubitron 50% −20 + 25, 800190.0 2.8 Substitute 321 50% −25 + 30 Comparative B No agglomeratesGrade 50 Cubitron ANSI G-50 N/A 262.3 3.2 (988CR) 222 loose grain 15Ferro 3227 Grade 50 Cubitron −18 + 20 750 289.8 6.9 321 16 Ferro 3227Grade 50 Cubitron 50% −20 + 25, 750 246.8 3.3 321 50% −25 + 30 17 Ferro3227 Grade 50 Cubitron −18 + 20 700 275.0 6.3 321 18 Ferro 3227 Grade 50Cubitron 50% −20 + 25, 700 231.5 3.5 321 50% −25 + 30 19 Ferro 3226Grade 50 Cubitron −18 + 20 850 258.9 5.7 321 20 Ferro 3226 Grade 50Cubitron 50% −20 + 25, 850 247.0 3.2 321 50% −25 + 30 20 Ferro 3225Grade 50 Cubitron −18 + 20 950 281.1 6.8 321 22 Ferro 3225 Grade 50Cubitron 50% −20 + 25, 950 256.8 3.8 321 50% −25 + 30 23 Ferro XF150Grade 50 Cubitron −18 + 20 850 265.0 4.5 321 24 Ferro XF150 Grade 50Cubitron 50% −20 + 25, 850 234.1 3.0 321 50% −25 + 30 25 Johns ManvilleTreibacher G800 −66 micron + 25 700 — — 2 inch fiberglass battsemi-friable alumina micron

1. An abrasive agglomerate comprising a plurality of abrasive grainsbonded together in a three-dimensional structure by a substantiallycontinuous, non-porous inorganic binder, wherein said abrasive grainshave an average size of between about 0.5 microns and about 1500microns, said inorganic binder comprises less than about 75 percent, byweight, of said agglomerate, wherein the bulk density of said abrasiveagglomerate is less than about 90 percent of the bulk density of saidabrasive grain, and wherein said abrasive grains, are not substantiallyencapsulated by said inorganic binder.
 2. (canceled)
 3. An abrasiveagglomerate according to claim 1, wherein said abrasive grains form adiscontinuous coating on said inorganic binder, wherein a straight lineextending radially outwardly from the center of said inorganic binderpasses through no more than three of said abrasive grains.
 4. Anabrasive agglomerate according to claim 3, wherein said straight linepasses through no more than 2 of said abrasive grains.
 5. An abrasiveagglomerate according to claim 1, wherein said abrasive grains form adiscontinuous monolayer on said inorganic binder.
 6. An abrasiveagglomerate according to claim 1, wherein said abrasive agglomerate hasan aspect ratio greater than 1:1.
 7. An abrasive agglomerate accordingto claim 1, wherein said abrasive agglomerate has an aspect ratio ofbetween about 1:1 and about 20:1.
 8. An abrasive agglomerate accordingto claim 1, wherein said abrasive grains are selected from the groupconsisting of fused aluninum oxide, ceramic aluminum oxide, beat treatedaluminum oxide, white fused aluminum oxide, brown fused aluminum oxide,monocrystalline fused aluminum oxide, silica, silicon carbide, greensilicon carbide, boron carbide, titanium carbide, alumina zirconia,fused alumina zirconia, diamond, ceria, cubic boron nitride, boronoxides in the form of B₆O and B₁₀O, garnet, tripoli, boron carbonitride,sintered alpha alumina-based abrasive particles, boehmite-derived,sintered alumina, and combinations thereof.
 9. An abrasive agglomerateaccording to claim 1, wherein said inorganic binder is a glass binder.10. An abrasive agglomerate according to claim 9, wherein said glassbinder is partially or completely crystallized.
 11. An abrasiveagglomerate according to claim 1, wherein said inorganic binder isselected from the group consisting of silicates, soda lime silicates,calcium silicates, calcium alumino silicates, sodium silicate, potassiumsilicates, borosilicates, phosphates, boron glasses, aluminates, glassceramics, titanate containing glasses, rare earth oxide glasses,zirconia based glasses, cullet and crushed post consumer recycled glass,and combinations thereof.
 12. An abrasive agglomerate according to claim1, wherein said abrasive agglomerate has a size between about 5 micronsand about 10,000 microns.
 13. An abrasive agglomerate according to claim1, comprising between about 3 and about 300 abrasive grains per abrasiveagglomerate.
 14. An abrasive agglomerate according to claim 1,comprising between about 0.05 grams and about 0.5 grams of the glassbinder per gram of said abrasive grains.
 15. A plurality of abrasiveagglomerates made by a process comprising: providing a plurality ofglass bodies, each glass body having a defined shape, said glass bodieshaving a softening temperature; providing a plurality of abrasivegrains; mixing said plurality of glass bodies with said plurality ofabrasive grains to form a mixture; heating said mixture to saidsoftening temperature so that said glass bodies soften whilesubstantially retaining said defined shape, and said abrasive grainsadhere to said softened glass bodies to form a plurality of abrasiveagglomerates wherein said abrasive grains are not substantiallyencapsulated by said glass bodies; and cooling said abrasiveagglomerates so that said glass bodies harden and said glass bodies aresubstantially continuous and non-porous after said cooling step.
 16. Aplurality of abrasive agglomerates according to claim 15, wherein saidplurality of glass bodies comprises a plurality of glass fibers. 17.(canceled)
 18. A coated abrasive comprising: a backing having a surface;and a plurality of abrasive agglomerates secured to said surface by abond system, each of said plurality of abrasive agglomerates including aplurality of abrasive grains bonded together in a three-dimensionalstructure by a substantially continuous, non-porous inorganic binder,wherein said abrasive grains have an average size of between about 0.5microns and about 1500 microns, said inorganic binder comprises lessthan about 75 percent, by weight, of the abrasive agglomerate, and thebulk density of said abrasive agglomerate is less than about 90 percentof the bulk density of the abrasive grains, and wherein said abrasivegrains are not substantially encapsulated by said inorganic binder. 19.A method of making a plurality of abrasive agglomerates comprising:providing a plurality of glass bodies, each glass body having a definedshape, said glass bodies having a softening temperature; providing aplurality of abrasive grains; mixing said plurality of glass bodies withsaid plurality of abrasive grains to form a mixture; heating saidmixture to said softening temperature so that said glass bodies softenwhile substantially retaining said defined shape, and said abrasivegrains adhere to said softened glass bodies to form a plurality ofabrasive agglomerates; and cooling said abrasive agglomerates so thatsaid glass bodies harden.
 20. A method according to claim 19, whereinsaid glass bodies are at least about 2 times larger than said abrasivegrains.
 21. A method according to claim 19, wherein the step ofproviding the plurality of abrasive grains includes providing excessabrasive grains.
 22. A method according to claim 19, wherein the step ofproviding the plurality of abrasive grains includes providing at leastabout 2 parts abrasive grains per 1 part glass bodies, by volume.
 23. Amethod according to claim 19, wherein the step of providing theplurality of abrasive grains includes providing at least about 4 partsabrasive grains per 1 part glass bodies, by volume.
 24. A methodaccording to claim 19, wherein the heating step include heating saidmixture to a temperature of between about 300° C. and about 1500° C. 25.A method according to claim 19, wherein the heating step includesheating said mixture to said softening temperature for between about 1hour and about 3 hours.
 26. A method according to claim 19, flithercomprising the step of separating said abrasive agglomerates from excessabrasive grains.
 27. A method according to claim 26, wherein theseparating step includes selecting a mesh screen having openings smallerthan said abrasive agglomerates and larger than said abrasive grains tosift said abrasive agglomerates from said excess abrasive grains.
 28. Amethod according to claim 19, further comprising the step of breakingsaid abrasive agglomerates into smaller sizes.